Ozone is a naturally occurring allotrope of oxygen. It has been known and used as an oxidant and disinfectant. In aqueous solutions, ozone is capable of killing bacteria in seconds at appropriate concentrations. It is often desirable to use ozone as a disinfecting or sanitizing agent as it imparts no odor and leaves no residue. The sanitizing properties of ozone dissolved in water, as well as its lack of odor and residue, make such a solution desirable to use for cleaning and disinfecting. Ozonated water can be used to disinfect or sanitize in both commercial and home settings. For example, ozonated water can be used to disinfect or sanitize bathroom counters, produce, dishes and cutlery, or floors.
One convenient method for using ozone as a disinfectant or sanitizer is to dissolve it in water or a water based solution. The stability of ozone is often a complicating factor in its use as a disinfecting or sanitizing agent since the high reactivity of ozone, which imparts its disinfecting and sanitizing properties, also results in reaction with reducing agents and, therefore, decomposition. Ozone in ozonated water, produced in anticipation of demand, will eventually decompose and return to being non-ozonated water.
Ozonation systems for producing ozonated water suitable for cleaning, disinfecting or sanitizing may be recirculating or non-recirculating systems.
Recirculating ozonation systems are designed with a tank of water and a recirculating ozonating flow path. The water flows through the ozonating flow path and dissolves an amount of ozone therein. Low efficiency in the ozonating flow path results in the need to recirculate the ozonated water back through the ozonation flow path in order to achieve the desired amount of dissolved ozone. This is typically achieved by recirculating the ozonated water back into the tank of water and running the ozonation system for a period of time until all the water in the tank is sufficiently ozonated.
Ozonation systems have addressed the delay between (a) starting the system and (b) delivery of ozonated water having a usable level of ozone, by increasing the efficiency of the ozonating flow path and/or by using a continuously recirculating system.
It is possible to produce ozonated water “on demand” using a continuously recirculating ozonation system. Continuously recirculating ozonation systems have an ozonation flow path that recirculates ozonated water back to the holding tank, and the system ozonates the water in the system regardless of whether ozonated water is being dispensed. In such systems, ozone is continuously added to the water to replace any ozone that has decomposed, or to ozonate any fresh water that has been added to replace ozonated water removed from the system. A steady-state of ozonated water is eventually reached based on the inlet and outlet flow rates, as well as the efficiency of the ozonation flow path used in the ozonation system. However, at the start of ozonation, the level of dissolved ozone is low and gradually increases until the steady-state is achieved.
It is also possible to use a non-recirculating ozonation system. Such systems dispense ozonated water “on demand” without the need for a continuously recirculating system. That is, non-recirculating ozonation systems dispenses ozone which has been added to the water via a single pass through the ozonating flow path, thereby doing away with the need for a holding tank.
In both recirculating and non-recirculating ozonation systems, regardless of whether the systems dispense ozonated water “on demand”, it is desirable to increase the concentration of dissolved ozone and reduce the rate of ozone decomposition.
Various factors impact the rate of ozone decomposition (Ericksson, M. “Ozone Chemistry in Aqueous Solution” 2005 Licentiate Thesis, Dept. of Chemistry, Royal Institute of Technology, Stockholm, Sweden; and Uhm H S, et al. “Increase in the ozone decay time in acidic ozone water and its effects on sterilization of biological warfare agents”, J. Hazard Mater. Sep. 15, 2009; 168(2-3):1595-601, epub Mar. 21, 2009). For example, increases in temperature, increases in speed of stirring, and higher ionic strength all accelerate the rate of ozone decomposition in aqueous solutions. In contrast, addition of radical scavengers or other stabilizers (for example, micellar surfactants), and decreasing the pH of the solution using acidic buffer systems, stabilize the ozone and reduce the rate of ozone decomposition.
Using distilled or deionized water (DI water) is understood to be beneficial when producing ozonated water. Ozonation systems that use corona discharge preferably use deionized water since ions present in tap water may “poison” the ozone cell and shorten its lifespan (see U.S. Pat. No. 6,964,739). One example of an ozonolysis system which uses DI water is the LIQUOZON® Ultra-Ozone Sanitization of DI Water Loop and Storage Tank, manufactured by MKS Instruments. The LIQUOZON® Ultra ozonated DI water unit is an automated ozone injection system used for the sanitization of process water systems, storage tanks and distribution lines.
It is desirable to provide a method and system for treating water so that, in comparison to untreated water, the average ozone decomposition rate in the treated water is reduced.